It is a well established fact that power plants perform better when ambient conditions allow for colder than normal condenser operation; cooler condenser temperatures allow for lower condenser pressures which together lead to greater power generation and thermodynamic efficiency. In fact, in certain circumstances this effect can be quite significant. Arrieta and Lora, in their paper “Influence of Ambient Temperature on Combined-Cycle Power-Plant Performance,” Applied Energy 80 (2005) 261-272, indicate that ambient conditions at or near freezing can lead to an 8.3% increase in net power generation compared to design conditions and up to a 16.7% increase in net power generation compared to hot temperature conditions.
Large regular swings in electricity demand between low load hours and peak load hours necessitate techniques for storing energy. There are currently only a few utility-scale energy storage technologies in existence; the most popular being pumped storage technology in which water is pumped up a hill during off-peak hours and run down like a hydro-electric plant during peak hours. Geographically, pumped storage has already reached its limits. Currently, to deal with the lack of storage options and the large differences in regular demand, small “peak loading” power plants are built. These power plants have the ability to turn on and off quickly, but operate only a few hours a day, so that they need to charge significantly higher rates for the electricity they produce.
Thermal energy storage concepts have been around for quite some time and a great deal of research continues in this area. Most commonly in power generation settings, thermal energy storage relies on heat stored in a substance at high temperature and insulated until it is desired to move heat from that high temperature substance to a working fluid. For example, in many solar thermal power plants, synthetic salts absorb heat energy during the daytime, and are used as a heat source to generate steam at night. These salts may also incorporate a phase transition between molten and solid states to increase their energy storage potential. Alternatives on this approach have been proposed such as Ellis et al. in their U.S. Patent Publication 2009-0179429, but they are still essentially similar in that storage technologies such as these are meant to be capable of running an entire power cycle without any assistance when they need to be called upon.
Hot temperature storage technologies are appropriate for situations like solar thermal plants where, without such energy storage options, the plant would be unable to operate at all during the night time. However, it is believed that such storage technologies are impractical for saving off-peak energy for peak hour consumption on a large scale. The reason for this is that in order to convert the heat energy stored in the medium into electricity, a dedicated set of power plant equipment is needed (i.e., a turbine, condenser, pumps, and the like). Along the same line of reasoning, the reason why hot temperature storage methods work for solar thermal plants is that without the storage system, the remainder of the plant equipment would be idle during night time. In the case of a fossil fuel fired power plant that runs twenty four hours a day, an additional power plant would have to be constructed to handle the stored energy.
Thermal energy storage can also come in the form of low temperature storage technologies. The most common low temperature storage systems involve creating ice or some higher temperature ice alternative during off-peak hours, and using the ice for air conditioning during peak hours instead of running a chiller. These systems are widely used in commercial settings but they are limited in their use. They are only used to supply cooling for air conditioning purposes, not for generation of electricity using a heat engine operating on a thermodynamic cycle.